In CMOS image sensors and other solid state image sensors, light receiving elements generate charges in accordance with the incident light. The charges stored in the light receiving elements are sequentially read out to acquire the image of the object to be captured. It is known that if the amount of light received becomes large, the charges end up becoming saturated at the light receiving elements and so-called “smear” occurs.
Patent Document 1 discloses a technique of providing two photodiodes at each pixel and lowering the charge (potential) of one photodiode by the charge (potential) of the other photodiode of surrounding pixels to prevent saturation of charges. Further, Patent Document 1 also discloses a technique of arranging the other photodiode immediately beneath the one photodiode.
Note that although not concerned with the technique of preventing saturation in the light receiving element, the technique of providing a photodiode on one principal surface of a substrate and, at the same time, providing a photodiode on the other principal surface is also known (Patent Documents 2 and 3).
Patent Document 1: Japanese Patent Publication (A) No. 2003-169252
Patent Document 2: Japanese Patent Publication (A) No. 5-243548
Patent Document 3: Japanese Patent Publication (A) No. 2004-103964